An organic electro-luminescence element (referred to below as [organic EL element]) using an organic electro-luminescence material can realize each emitted color of light in the visible light band from white emitting light by selecting and organic material or by adopting a structure of an organic EL element. As a result, the development of display devices and lighting equipment which use organic EL elements is progressing.
An organic EL display device is arranged with an organic EL element in each pixel, the organic EL element in each pixel is connected to a transistor and emitted light is controlled via this transistor. The organic EL element is formed in an element substrate formed with a transistor. In the structure of a pixel, an interlayer insulation layer is generally arranged between the organic EL element and the transistor. In addition, one electrode which forms the organic EL element and a source/drain electrode of a transistor are electrically connected in a contact hole formed in the insulation layer.
An organic EL display device includes a pixel array arranged with this type of pixel in a matrix shape and light emitted from the organic EL element is emitted to the side of the element substrate or an opposing substrate arranged facing the element substrate and thereby a display surface is formed on the surface.
This type of organic EL element is arranged with a layer (referred to below as [organic electro-luminescence layer] or [organic EL layer]) including an organic electro-luminescence material between a pair of electrodes called an anode and cathode. Since light emitted by the organic EL layer spreads in all 4 π directions when expressed as a solid angle, there is a problem in effectively using light emitted in directions apart from the display screen side.
In addition, there is a problem whereby light irradiated in a parallel direction within the organic EL layer is irradiated from a transparent electrode side towards the end surface of the organic EL layer. This is because the refractive index of a material which forms the organic EL layer is high (n=1.8˜1.9) and all the light which is irradiated at a specific angle at an interface with a difference refractive index is reflected. For example, all the light reflected at an interface between an organic EL layer and a transparent electrode, and between a glass substrate and air is either wave guided within the organic EL layer or glass substrate and absorbed with the layer or is emitted from the end surface of the glass substrate.
It is said that the extraction ratio (ratio of the amount of light irradiated to the glass substrate side as a proportion of the total amount of light in the organic EL layer) of light generated by an organic EL layer is about 20% due to light being wave guided within the organic EL layer in this way. It is important to increase the extraction ratio of light generated by an organic EL layer in order to reduce power consumption of an organic EL display device formed using an organic EL element.
Therefore, in a conventional organic EL display device, a diffraction grating comprised from a concave layer is formed above a transparent electrode, a transparent electrode, organic EL layer and metal electrode are stacked in order above the diffraction grating to form an organic EL element in order to attempt to improve the extraction ratio of light using the diffraction effects caused by the concave shape diffraction grating (for example, refer to Japanese Laid Open Patent 2013-109932).
However, according to the conventional organic EL display device described in the patent document mentioned above, it was necessary to manufacture an uneven shaped diffraction grating so that an uneven wavenumber and an uneven depth distribution etc in a Fourier transformed image have a constant numerical value, and because a high level of precision is demanded in the manufacturing process, there was a danger that the manufacturing process would become complex and manufacturing costs would increase.
In addition, according to a conventional organic EL display device, in a pixel arranged with an organic EL element, there is a danger that mixing of colors may occur when light emitted in a diagonal direction of a pixel becomes leaked light emitted from an adjacent pixel. However, the aperture ratio of a pixel decreases when the width of a light shielding layer which sections a region of a pixel is increased in order to reduce the effects of mixing colors, and there is danger that light emitted from an organic EL element cannot be used effectively.
Therefore, the present invention aims to effectively use light emitted from an organic EL element as light emitted in each pixel in an organic EL display device. In addition, it is an aim of the present invention to realize a simple structure which improves the extraction ratio of light from each pixel without significantly changing the manufacturing process.